Jason Cline

DMD-based adaptive spectral imagers for hyperspectral imagery and direct detection of spectral signatures

Dispersive transform spectral imagers with both one- and two-dimensional spatial coverage have been demonstrated and characterized for applications in remote sensing, target classification and process monitoring. Programmable spatial light modulators make it possible to adjust spectral, temporal and spatial resolution in real time, as well as implement detection algorithms directly in the digitally controlled sensor hardware. Operating parameters can be optimized in real time, in order to capture changing background and target evolution. Preliminary results are presented for short wave, mid-wave, and long-wave infrared sensors that demonstrate the spatial and spectral versatility and rapid adaptability of this new sensor technology.

Programmable Adaptive Spectral Imagers for Mission-Specific Application in Chemical/Biological Sensing

An innovative passive standoff system for the detection of chemical/biological agents is described. The spectral, temporal and spatial resolution of the data collected are all adjustable in real time, making it possible to keep the tradeoff between the sensor operating parameters at optimum at all times. The instrument contains no macro-scale moving parts and is therefore an excellent candidate for the development of a robust, compact, lightweight and low-power-consumption sensor. The design can also serve as a basis for a wide variety of spectral instruments operating in the visible, NIR, MWIR, and LWIR to be used for surveillance, process control, and biomedical applications.

Direct Simulation Monte Carlo Investigation of Hyperthermal Oxygen Beam Exposures

Pulsed sources of hyperthermal O-atoms are now being extensively used to simulate low-Earth-orbit (LEO) surface exposure environments. The peak flux of these sources is many orders of magnitude larger than the corresponding LEO flux. Although it is desirable to accelerate the test by using higher fluxes than found in LEO, even commonly used fluxes are large enough to produce multicollision effects by causing a buildup of gas at the sample surface. We characterize the physical consequences to the experiment using the direct simulation Monte Carlo (DSMC) method. DSMC allows us to extract the distributions of energy and impact angle for the O-atoms that reach the surface and to record how strongly the gas buildup at the target assembly deflects flux from downstream instrumentation. By considering a range of source fluxes, we determine the onset conditions and severity of these multicollision effects. We find that, depending on the target properties, even at common experimental fluxes with a normally incident beam striking a flat surface sample, the energy distribution of incident O-atoms can broaden and develop a significant low-energy tail. The distribution of the angle of impact can also broaden significantly, and the number of O-atoms that reach downstream instrumentation can be attenuated by as much as ∼50%. These simulations will aid in the calibration of ground-based O-atom measuremehts and provide a model for the energy and angular distributions of O-atoms that actually impinge on surface samples.

A passive optical technique to measure physical properties of a vibrating surface

We report on a passive imaging technique to measure physical properties of a vibrating surface using the detection of optical signal modulation in light scattered from that surface. The optical signal modulation arises from a changing surface normal and may be used to produce a surface normal change image without touching the surface and changing its state. The images may be used to extract the surface vibration frequency and mode pattern which are dependent on surface properties of the material, including its flexural modulus and mass density. Comparison of the vibration image with a finite element model may be used to infer properties of the vibrating surface, including boundary conditions. A temporal sequence of optical images of signal modulation may be analyzed to infer spatial damping properties of the surface material. Damping is a measure of energy dissipation within the material. The approach being developed has the advantage of being able to remotely image arbitrary sized structures to determine global or local vibrational properties.

Transient Modeling of High-Altitude Rocket-Stage Separation

Abstract : The direct simulation Monte Carlo method is used to model a transient stage separation of a generic sounding rocket at 100 km. Lower stage movement is included, and the flow and surface properties are simulated over the first second after thruster ignition. Both liquid and solid propellant thrusters are examined with a thrust of 25 kN and 34 kN, respectively. Four different simulation scenarios are considered that allow analysis of the impact of the stage motion, explicitly including unsteady flow effects. Unsteady flow effects are small enough that quasi-steady state modeling appears to be adequate for this general staging scenario. The influence of DSMC statistical fluctuations on the stage trajectory is insignificant compared to the total contribution of the plume force. We also examine the radiation environment, including the plume-atmosphere shock and plume-lower stage impingement.

Simulation framework for space environment ground test fidelity

We present initial work to develop an extensible model for spacecraft environmental interactions. The starting point for model development is a rarefied gas dynamics model for hyperthermal atomic oxygen. The space envi- ronment produces a number of challenging stimuli, including atomic oxygen, but also charged particles, magnetic fields, spacecraft charging, ultraviolet radiation, micrometeoroids, and cryogenic temperatures. Moreover, the responses of spacecraft to combinations or sequences of these stimuli are different from their responses to single stimuli. New multi-stimulus test facilities such as the Space Threat Assessment Testbed at the USAF Arnold Engi- neering Development Complex make understanding the similarities and differences between terrestrial test and on-orbit conditions increasingly relevant. The extensible model framework under development is intended to host the variety of models needed to describe the multiphysics environment, allowing them to interact to produce a consistent unified picture. The model framework will host modules that can be validated individually or in combination.

Passive Optical Detection of a Vibrating Surface

Abstract : A new light-intensity modulation technique arising from a changing surface normal can measure the physical properties of a vibrating surface.

A compact, thermal-infrared spectral imager for chemical-specific detection

A second-generation long-wave hyperspectral imager based on micro-electro-mechanical systems (MEMS) technology is in development. Spectral and spatial encoding using a MEMS digital micro-mirror device enables fast, multiplexed data acquisition with arbitrary spectral response functions. The imager may be programmed to acquire spectrally selective contrast imagery, replacing more time-consuming hyperspectral data collection. A single-element detector collects encoded data and embedded real-time hardware generates imagery. An internal scanning mechanism enables rapid retrieval of full hyperspectral imagery. The resulting rugged, low-cost sensor will provide chemically specific imagery for applications in gaseous and surface contaminant detection, surveillance, remote sensing, and process control.

Turbine Engine Temperature Pattern Factor Control System Based on Fuel Modulation and Passive Optical Sensors

We present preliminary results for a new passive optical sensor that is the basis for a temperature pattern factor control system. The sensor uses the natural combustion radiance in several spectral bands to deduce the local pre-combustion equivalence ratio, which is correlated with local combustor exit temperature. The sensor was applied in an arc-sector combustor and in a closed-loop control system in a four-way laboratory burner.

Development of the ARISTOTLE webware for cloud-based rarefied gas flow modeling

Rarefied gas dynamics are important for a wide variety of applications. An improvement in the ability of general users to predict these gas flows will enable optimization of current, and discovery of future processes. Despite this potential, most rarefied simulation software is designed by and for experts in the community. This has resulted in low adoption of the methods outside of the immediate RGD community. This paper outlines an ongoing effort to create a rarefied gas dynamics simulation tool that can be used by a general audience. The tool leverages a direct simulation Monte Carlo (DSMC) library that is available to the entire community and a web-based simulation process that will enable all users to take advantage of high performance computing capabilities. First, the DSMC library and simulation architecture are described. Then the DSMC library is used to predict a number of representative transient gas flows that are applicable to the rarefied gas dynamics community. The paper closes with a summary...